PROJECT SUMMARY Viral encephalomyelitis is the inflammation of the brain and spinal cord caused by viral infection. Viral encephalomyelitis is of significant public health concern due to its high mortality rate and association with permanent neurologic sequelae following damage of mature, post-mitotic neurons. In spite of its potentially devastating effects, there are few vaccines and no targeted treatments available. A critical gap in our knowledge is how virus is cleared from infected neurons without damaging the host neuron during recovery. Using the Sindbis virus (SINV) rodent encephalomyelitis model, we identified a mechanism of antibody- mediated, non-cytolytic viral clearance in infected neurons that leaves the host neuron functionally intact and likely plays a key role in recovery from viral encephalomyelitis. Although antibody and immune cells do not normally cross the blood-brain barrier (BBB), neuroinflammatory SINV infection results in loss of BBB intregrity and increased expression of intercellular adhesion molecules that promote leukocyte transmigration. Specifically, antibody binding of SINV E2 glycoprotein on the plasma membrane of infected neurons suppresses viral replication in vitro in a dose-dependent manner, although the precise mechanism is not known. Antibody must be bivalent to be efficacious, does not require other effector cell types, does not enter the cell, and is only protective in mature neurons. We hypothesize that extracellular antibody crosslinking of E2 on the plasma membrane of infected neurons induces an intracellular signaling cascade that results in a host antiviral response. To determine the signaling pathways activated during antibody-mediated clearance and gain insight into its mechanism, we performed a high throughput signaling activation screen. We discovered that anti-E2 antibody treatment, in comparison with mock or antibody isotype control (anti-SINV E1 glycoprotein), resulted in immediate transient NF?B signaling and late sustained STAT3 activation. Additional studies revealed that anti-E2 induces rapid increased expression of the neuropoeitic IL-6 family cytokine LIF, a NFkB target gene and potent inducer of STAT3. These data outline a potential antibody-induced autocrine/paracrine signaling cascade and suggest that STAT3 is an important mediator of viral clearance. The goal of this proposal is to determine how antibody against SINV E2 induces non-cytolytic clearance of SINV from persistently infected mature neurons. Guided by our preliminary data, we propose to pursue two Specific Aims: 1) To determine the role of LIF cytokine in antibody-induced cellular signaling, and 2) To determine the function of prolonged STAT3 activation (transcriptional or microtubule dysregulation) in antibody-mediated viral clearance. Elucidation of the antibody-mediated, non-cytolytic viral clearance mechanism will have significant implications for the development of novel vaccines and therapeutics against alphaviral encephalomyelitis.